The goalkeeper, who has represented England at Under-16, Under-17 and Under-19 level, has committed his future to the stamford Bridge side until June 2019.
Blackman has been at the West London club since the age of 13 and he was an ever-present during the triumphant FA Youth Cup campaign in 2011/12.
He was part of the first-team squad last season, training regularly alongside Petr Cech and Mark Schwarzer and he featured in a friendly against Manchester City in the US last May.
Blackman will be hoping to progress even further this year, as he will no doubt be aiming to catch the eye of England U21 boss Gareth Southgate and add to his international caps.
Written by Steve Milne